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Elucidating the variation of allocation pattern of ecosystem net primary productivity (NPP) and its underlying mechanisms is critically important for understanding the changes of aboveground and belowground ecosystem functions. Under optimal partitioning theory, plants should allocate more NPP to the organ that acquires the most limiting resource, and this expectation has been widely used to explain and predict NPP allocation under changing precipitation. However, confirmatory evidence for this theory has mostly come from observed spatial variation in the relationship between precipitation and NPP allocation across ecosystems, rather than directly from the influences of changing precipitation on NPP allocation within systems. We performed a 6-yr five-level precipitation manipulation experiment in a semiarid steppe to test whether changes in NPP allocation can be explained by the optimal partitioning theory, and how water requirement of plant community is maintained if NPP allocation is unaltered. The 30 precipitation levels (5 levels × 6 yr) were divided into dry, nominal, and wet precipitation ranges, relative to historical precipitation variation over the past six decades. We found that NPP in both aboveground (ANPP) and belowground (BNPP) increased nonlinearly as precipitation increased, while the allocation of NPP to BNPP (f BNPP) showed a concave quadratic relationship with precipitation. The declined f BNPP as precipitation increased in the dry range supported the optimal partitioning theory. However, in the nominal range, NPP allocation was not influenced by the changed precipitation; instead, BNPP was distributed more in the surface soil horizon (0–10 cm) as precipitation increased, and conversely more in the deeper soil layers (10–30 cm) as precipitation decreased. This response in root foraging appears to be a strategy to satisfy plant water requirements and partially explains the stable NPP allocation patterns. Overall, our results suggest that plants can adjust their vertical BNPP distribution in response to drought stress, and that only under extreme drought does the optimal partitioning theory strictly apply, highlighting the context dependency of the adaption and growth of plants under changing precipitation.

Aims Exploring the relationships between water uptake, fine root, and soil water is essential for many fields, such as plant physiology, ecological hydrology, and water conservancy. Methods In four Populus tomentosa stands with different ages (young and mature) and stand structures (low and high stand density), we matched root water uptake patterns obtained from stable isotope techniques with fine root and soil water distributions, respectively. The effects of soil water content and meteorological factors on these matching degrees were further explored. Results Increased competition intensity within a stand would suppress the matching degree between fine root distribution and water uptake pattern ( M FR ), but have little effect on the matching degree between soil water distribution and water uptake pattern ( M SR ). Additionally, water uptake pattern was closer to soil water distribution (average M SR were 0.89) than to fine root distribution in mature stands (average M FR were 0.68), while water uptake pattern matched both fine root and soil water distribution closely in young stands (average M FR and M SR were 0.89 and 0.83). There is a relatively high positive or negative correlation between M FR and M SR in all four stands. Compared with the direct effect of soil water content, the influence of meteorological factors on matching degrees was weak. Conclusion The results indicate that the expression of water uptake function of the young stand depends on a combination of root structure and available water resources, while the water uptake function of mature stands is driven more by available water resources rather than root structure.

Aims Plant roots control many important interactions in the wetland anoxic zone such as carbon deposition, gas exchange, and nutrient dynamics, yet few studies document the vertical depth distribution of fine roots which mediates these interactions. Methods Excavated root systems of a wetland sedge and shrub were scanned. Utilizing Root System Analyzer, normalized root length per 5 cm depth interval were quantified for 10 samples of each species. Utilizing bootstrapping, root length per depth interval for each root class was fitted to a density distribution function and matched to water table depth. Results Vertical root length distributions varied by root class, with shrub fine roots constrained to a narrow depth range. Between 1999 and 2010, the interface with the anoxic zone can vary by a factor of four between wet and dry years. Conclusions Compared to estimates of root vertical distribution based on biomass, this study indicates a considerably higher portion of the fine roots occur in anoxic soil. Accurately quantifying the spatial distribution of the fine roots, root tips, and other sites associated with exudation is crucial for determining the strength of root-methanogen interactions.

1. Climate warming is faster in the Arctic than the global average. Nutrient availability in the tundra soil is expected to increase by climate warming through (i) accelerated nutrient mobilization in the surface soil layers, and (ii) increased thawing depths during the growing season which increases accessibility of nutrients in the deeper soil layers. Both processes may initiate shifts in tundra vegetation composition. It is important to understand the effects of these two processes on tundra plant functional types. 2. We manipulated soil thawing depth and nutrient availability at a Northeast-Siberian tundra site to investigate their effects on above- and below-ground responses of four plant functional types (grasses, sedges, deciduous shrubs and evergreen shrubs). Seasonal thawing was accelerated with heating cables at c. 15 cm depth without warming the surface soil, whereas nutrient availability was increased in the surface soil by adding slow-release NPK fertilizer at c. 5 cm depth. A combination of these two treatments was also included. This is the first field experiment specifically investigating the effects of accelerated thawing in tundra ecosystems. 3. Deep soil heating increased the above-ground biomass of sedges, the deepest rooted plant functional type in our study, but did not affect biomass of the other plant functional types. In contrast, fertilization increased above-ground biomass of the two dwarf shrub functional types, both of which had very shallow root systems. Grasses showed the strongest response to fertilization, both above- and below-ground. Grasses were deep-rooted, and they showed the highest plasticity in terms of vertical root distribution, as grass root distribution shifted to deep and surface soil in response to deep soil heating and surface soil fertilization respectively. 4. Synthesis. Our results indicate that increased thawing depth can only benefit deep-rooted sedges, while the shallow-rooted dwarf shrubs, as well as flexible-rooted grasses, take advantage of increased nutrient availability in the upper soil layers. Our results suggest that grasses have the highest root plasticity, which enables them to be more competitive in rapidly changing environments. We conclude that root vertical distribution strategies are important for vegetation responses to climate-induced increases in soil nutrient availability in Arctic tundra, and that future shifts in vegetation composition will depend on the balance between changes in thawing depth and nutrient availability in the surface soil.

Vegetation roots play a pivotal role in enhancing the shear resistance and stability of degraded mountain red soils, yet the quantitative effects of root density and orientation remain poorly constrained. In this study, unconsolidated undrained triaxial tests were conducted on red soil reinforced with Acacia dealbata roots to examine the influence of root area ratio (RAR), spatial arrangement, and confining pressure on stress–strain behaviour and shear strength. Shear strength parameters were derived from Mohr–Coulomb envelopes, and the increments in cohesion (Δc) and internal friction angle (Δ φ ) were analytically related to the increment of the major principal stress (Δσ₁). The results indicate that the presence of root systems enhanced both peak strength and the reinforcement index. The configuration with high RAR and horizontal root distribution achieved up to 64.80% higher deviator stress than the unreinforced control, whereas sparse vertical roots could weaken the composite under low confinement. Reinforcement efficiency was governed by the combined effects of root density and orientation, with dense, horizontally distributed networks most effectively mobilising interfacial friction and tensile resistance. Strength envelopes indicated simultaneous increases in apparent cohesion and internal friction angle, where Δc contributed nearly linearly to Δσ₁, while Δ φ induced a quadratic amplification; their synergistic effect was further enhanced at higher confining pressures. This study provides robust experimental evidence and a quantitative framework to inform eco-engineering and slope stabilisation practices in mountain red soils, highlighting the importance of root system density and architecture in maximising vegetation-based reinforcement.

This study investigates the effects of root distributions and stress paths on the shear strength of root-soil composites using a consolidated-undrained (CU) triaxial test. On the basis of the limit equilibrium, two root reinforcement coefficients (n and m) are proposed for characterizing the effects of shear strength parameters on the principal stress considering different root distribution angles and root diameters. Then, n and m are introduced into the conventional limit equilibrium equation to develop a new limit equilibrium equation for root-soil composites. The results demonstrate that the root distribution angles (α) and root diameters (d) affect the shear strength of the root-soil composites. Under a consolidated-undrained condition, the effective cohesion (crs′) of the rooted soil is high and decreases in the order of 90°, 0°, 30° and 60°. For the same root distribution angle, crs′ increases with the increasing root diameter. Meanwhile, the effective internal friction angle (φrs′) changes slightly. The failure principal stress of the root-soil composites is positively correlated with n and m. Furthermore, the deformation of the samples indicates that the run-through rate of α = 90° and α = 0° are both 0. Meanwhile, the lateral deformation rate declines from 17.0% for α = 60° to 10.9% for α = 90°.

Shallow soils are highly vulnerable to the combined impacts of various factors, including vehicle loading, precipitation, and groundwater. The slope soil at the roadside is inevitably subjected to long-term cyclic loading from traffic. Previous studies have demonstrated that ecological engineering measures can effectively mitigate soil deformation and reduce pore water pressure development, thereby preventing soil erosion and landslides. This study aims to investigate the influence of root distribution patterns on the elastic deformation and pore water pressure development trends in root reinforced soil by simulating cyclic traffic loading through dynamic triaxial tests. The study findings demonstrate that the presence of roots significantly enhances the soil’s resistance to deformation. When the vertical root accounts for 25% (while the horizontal root accounts for 75%), experimental results indicate that the soil reinforced by roots exhibits minimal deformation and slower pore water development. Moreover, a parameter D is introduced to enhance the existing pore water pressure models with the increased coefficients of determination, thereby improving the applicability in root-reinforced soils. These findings provide valuable insights for enhancing strength and liquefaction resistance in root reinforced soils while providing guiding research for the mechanical effects of root reinforcement of soil for ecological restoration of highway slopes.

BACKGROUND AND AIMS: Water availability is often one of the most limiting factors for plants. Climate change predictions for many areas suggest an intensification of water limitation. The ability of a plant to modify its root characteristics can be an important mechanism for preventing drought stress. METHODS: We studied the drought response of seedlings of 10 woody species and compared the biomass allocation, vertical root distribution across different root diameters, and the key traits of very fine roots (root diameter <0.5 mm) under two water regimes (no water limitation and severe drought). RESULTS: Under drought conditions, the very fine roots had a higher specific root length (SRL, root length: biomass ratio), smaller root diameter and higher root tissue mass density, as well as a lower nitrogen concentration. A higher value of the mean root plasticity index was related to higher drought resistance. A quantitative literature review showed that there was a wide variation in the effect of the drought on SRL, thus there was not a clear effect of drought on SRL. CONCLUSIONS: Certain species have the necessary root traits and plasticity to survive drought. We have identified plasticity in root characteristics as a whole-plant trait which plays a significant role in separating out species into those which are vulnerable and those which are resistant to drought.

Even though ecologists and agronomists have considered the spatial root distribution of plants to be important for interspecific interactions in natural and agricultural ecosystems, few experimental studies have quantified patterns of root distribution dynamics and their impacts on interspecific interactions. A field experiment was conducted to investigate the relationship between root distribution and interspecific interactions between intercropped plants. Roots were sampled twice by auger and twice by the monolith method in wheat (Triticum aestivum L.)/maize (Zea mays L.) and faba bean (Vicia faba L.)/maize intercropping and in sole wheat, maize, and faba bean up to 100 cm depth in the soil profile. The results showed that the roots of intercropped wheat spread under maize plants, and had much greater root length density (RLD) at all soil depths than sole wheat. The roots of maize intercropped with wheat were limited laterally, but had a greater RLD than sole-cropped maize. The RLD of maize intercropped with faba bean at different soil depths was influenced by intercropping to a smaller extent compared to maize intercropped with wheat. Faba bean had a relatively shallow root distribution, and the roots of intercropped maize spread underneath them. The results support the hypotheses that the overyielding of species showing benefit in the asymmetric interspecific facilitation results from greater lateral deployment of roots and increased RLD, and that compatibility of the spatial root distribution of intercropped species contributes to symmetric interspecific facilitation in the faba bean/maize intercropping.

There is little direct evidence for effects of soil heterogeneity and root plasticity on the competitive interactions among plants. In this study, we experimentally examined the impacts of temporal nutrient heterogeneity on root growth and interactions between two plant species with very different rooting strategies: Liquidambar styraciflua (sweet gum), which shows high root plasticity in response to soil nutrient heterogeneity, and Pinus taeda (loblolly pine), a species with less plastic roots. Seedlings of the two species were grown in sandboxes in inter‐ and intraspecific combinations. Nutrients were applied in a patch either in a stable (slow‐release) or in a variable (pulse) manner. Plant aboveground biomass, fine root mass, root allocation between nutrient patch and outside the patch, and root vertical distribution were measured. L. styraciflua grew more aboveground (40% and 27% in stable and variable nutrient treatment, respectively) and fine roots (41% and 8% in stable and variable nutrient treatment, respectively) when competing with P. taeda than when competing with a conspecific individual, but the growth of P. taeda was not changed by competition from L. styraciflua. Temporal variation in patch nutrient level had little effect on the species’ competitive interactions. The more flexible L. styraciflua changed its vertical distribution of fine roots in response to competition from P. taeda, growing more roots in deeper soil layers compared to its roots in conspecific competition, leading to niche differentiation between the species, while the fine root distribution of P. taeda remained unchanged across all treatments. Synthesis. L. styraciflua showed greater flexibility in root growth by changing its root vertical distribution and occupying space of not occupied by P. taeda. This flexibility gave L. styraciflua an advantage in interspecific competition. Liquidambar styraciflua showed greater flexibility in root growth by changing its root vertical distribution and occupying space not occupied by Pinus taeda. This flexibility gave L. styraciflua an advantage in interspecific competition.